It is often desirable to know the location of a terminal such as a cellular phone. For example, a location services (LCS) client may desire to know the location of a terminal in the case of an emergency services call or to provide some service to the user of the terminal such as navigation assistance or direction finding. The terms “location” and “position” are synonymous and are used interchangeably herein.
In Observed Time Difference of Arrival (OTDOA) based positioning, the mobile station may measure time differences in received signals from a plurality of base stations. Because positions of the base stations are known, the observed time differences may be used to calculate the location of the terminal. To further help location determination, Positioning Reference Signals (PRS) are often provided by a base station (BS) in order to improve OTDOA positioning performance. The measured time difference of arrival of the PRS from a reference cell (e.g. the serving cell) and one or more neighboring cells is known as the Reference Signal Time Difference (RSTD). Using the RSTD measurements, the absolute or relative transmission timing of each cell, and the known position(s) of BS physical transmitting antenna element(s) for the reference and neighboring cells, the UE's position may be calculated.
However, when Base Stations (BS) use multiple physical transmitting antenna elements and the physical transmitting antenna elements are switched between PRS occasions, UE's that utilize multiple PRS occasions and coherent averaging/integration over the multiple PRS occasions to determine a Time of Arrival (TOA) value may obtain incorrect results because different propagation channels may have been used for different PRS occasions. Similarly, in a conventional distributed antenna system (DAS) spatially separate physical transmitting antenna elements, which belong to the same cell and share the same cell Physical Cell Identifier (PCI), transmit the same PRS signal. Consequently, in conventional DAS, the location of the signal transmitter in the DAS case may be ambiguous, and UE position calculation may be erroneous or not be possible. Position calculation is also ambiguous in traditional systems using low power Remote Radio Heads (RRHs) or small cells (e.g. femtocells) within a macrocell coverage area because the transmission points created by the spatially separate RRHs or small cells may have the same PCIs as the macro cell and consequently transmit identical PRS signals.